A method for inserting a catheter or vascular sheath into a blood vessel involves the use of the Seldinger technique, which includes an access needle that is inserted into a patient's blood vessel. A guidewire is inserted through the needle and into the vessel. The needle is removed, and a dilator and sheath combination are then inserted over the guidewire. The dilator and sheath combination is then inserted a short distance through the tissue into the vessel. The combination of the needle, dilator, and sheath, can be advanced over the guidewire into the blood vessel. After this combination has been advanced, the dilator is removed. The catheter is then inserted through the sheath into the vessel to a desired location. The Seldinger technique, and variations thereof, and devices used to perform this technique, are described in Seldinger (1953) Acta Radiologica 39:368-376; U.S. Pat. No. 7,722,567 issued to Tal, U.S. Pat. No. 7,972,307 issued to Kraus, et al, and U.S. Pat. No. 7,938,806 issued to Fisher, et al, which are incorporated by reference. U.S. Pat. No. 6,004,301 issued to Carter provides several elementary diagrams that disclose the insertion of a needle through the patient's flesh, with insertion into a blood vessel. Dilator finds use, for example, to minimize trauma to the patient during insertion of the sheath. Following dilation of the vasculature, dilator is withdrawn and replaced with a desired ancillary medical device, for example, a catheter. Dilator also finds use, where sheath is very flexible, and where the target pathway is very tortuous, and here a dilator is used to facilitate advancing the sheath through the tortuous pathway to the target area (U.S. Pat. No. 7,303,552 of Chu, which is incorporated by reference in its entirety).
If the catheter to be inserted is significantly larger than the guide wire, a sheath (sometimes called “introducer sheath”) with a dilator contained inside is passed over the guidewire to enlarge the vessel incision hole. After the incision hole is sufficiently enlarged, the dilator is removed, leaving the sheath and guidewire in position inserted into the incision hole. The guidewire is also usually removed with the dilator. Insertion guidewires are usually not long enough to pass the catheter over. The catheter may come with a wire stylet as a secondary guidewire. Often, the guidewire is removed with the dilator, that is, the guidewire is not left inserted in the incision hole. The catheter is then inserted into the sheath, through the incision hole and into the blood vessel, and the sheath is then removed from around the exterior of the catheter.
When removing the sheath, and where a catheter or other device needs to remain within the sheath and needs to remain within the blood vessel, removal of the sheath is made possible by using a splittable sheath, sometimes called peelable or tearaway sheath.
The sheath that can be split away from the catheter as the sheath is being removed from the patient greatly facilitates the removal of the sheath. By splitting the sheath along its longitudinal axis as the sheath is being removed from the patient, the practitioner can pull out the sheath in such a way that the sheath can be removed without interfering with the catheter, or with any accessories, fittings, clamps, that are part of the catheter. See, e.g., U.S. Pat. No. 7,938,806 issued to Fisher, et al, which is incorporated herein in its entirety.
Where a sheath includes a hub, the hub serves as a handle (wings; tabs), and as a mating point for the insertion and locking of the dilator device. When the sheath needs to be split apart to be successfully withdrawn from the patient's body while leaving the catheter in place, the hub will also have to be split apart in order to clear the catheter. Sheath splitting is necessary, for example, where the catheter has any encumbrance, such as a hub on its proximal end (see, e.g., U.S. Pat. No. 7,422,571 issued to Schweikert and Nardeo, which is incorporated herein by reference).
A dilator is often used to aid in the insertion of the sheath. The dilator can have a long tubular section, the outside diameter of which can be slightly smaller than the inside diameter of the sheath. The dilator also has a pointed tip on its distal end and a hollow longitudinal passageway running the entire length thereof. The dilator is inserted into the patient's body through the sheath along the guide wire, allowing the distal tip to extend into the incision hole, carefully enlarging it. The dilator is then removed along the guide wire prior to insertion of the catheter along the guide wire and into the sheath. The guidewire is also usually removed with the dilator, as mentioned above. In many clinical situations, the guidewire is removed with the dilator, that is, where the guidewire is not left inserted in the incision hole.
However, after the dilator is removed, and before the catheter is inserted through the sheath, the sheath becomes an open conduit, allowing blood to leak or ooze from the vessel through the sheath or allowing air to be aspirated into the vessel through the sheath, neither of which is desirable. The practitioner conventionally has had to place a thumb or finger over the proximal opening of the sheath to prevent blood loss and air embolism. Alternatively, the device can include a valve for preventing blood loss, air emboli, or exposure to blood borne pathogens. Regarding air emboli, air entry through negative pressure differential can cause a build-up of air bubbles, leading to air embolisms in the ventricle. For example, a valve can be configured to automatically close and seal the opening as soon as the dilator is removed. The valve can seal around the guidewire, dilator, and catheter, as well as cause a seal where the sheath does not contain any other medical device. Valve finds use, e.g., where blood pressure makes backflow of blood through the sheath a problem (U.S. Pat. No. 7,303,552 to Chu, which is incorporated herein in its entirety).
Following insertion of the sheath and removal of the dilator, the sheath body forms a conduit for inserting a catheter or other medial articles.